Study On Catalytic Performance Of Catalysts Pd/Mn_X Zr_1-xO₂ Supported On Cordierite Honeycomb For Toluene In A Reverse Flow Reactor

The air pollution caused by VOCs emissions has drawn considerable attention in recent years. Compared with the traditional fixed bed catalytic combustion technology, the reverse flow catalytic combustion technique is a unique solution in respect to the elimination of VOCs.Catalytic combustion of VOCs in a reverse flow reactor (RFR) has high integrity and high recovery efficiency, even the inlet temperature and pollutant concentration of waste gas are very low, the reactor can be operated autothermally. The reactor has high stability even the feed composition and gas velocity fluctuate frequently in a certain range.In this work, using air containing toluene as the simulation of industrial emissions, low-temperature catalytic activity of catalyst and operating parameters of RFR are systematically studied. On one hand, catalysts Pd/MnxZr1-xO2 supported on cordierite honeycomb carrier, were prepared by an equal volume impregnation method and characterized by BET, SEM, XRD and Raman spectroscopy. The effect of different ratios of Mn/Zr on catalytic combustion of toluene, preparation conditions etc were investigated. On the other hand, in the reverse flow catalytic combustion system,the effects of operational parameters such as space velocity,toluene concentration and period duration on the shape of heat waves and the characteristic parameters such as peak temperature, average temperature were investigated. The main conclusions are as follows:1. The results of catalysts Pd/MnxZr1-xO2 supported on cordierite honeycomb carrier characterization indicated that the washcoat loaded uniformly and the washcoat is showed strong adhesion to cordierite. The different ratios of Mn/Zr had little influence on the specific surface area of the catalysts. The increasing grain of palladium oxide may be the main reason leading to lower catalyst activity if the reaction is in the high temperatures. The results of catalytic combustion of toluene showed that the catalyst Pd/ Mn0.4Zr0.6O2 supported on cordierite honeycomb carrier, calcined at 600℃exhibited the highest activities in the experimental conditions of 400 mg/m3 of toluene concentration and 4000 h-1 of space velocity , the conversion of toluene reached 95% at the reaction temperature of 280℃.2. For the catalysts Pd/Mn0.4Zr0.6O2/cordierite , the addition of citric acid complexing agent may be appropriate to improve the catalytic activity; Lower calcination temperature, the catalytic combustion efficiency improved with increasing calcination temperature,if the temperature is too high, the catalyst will be part of the sintering and catalytic activity decreased;When the quality score of palladium content was 0.8%, the catalysts had the highest catalytic activity.Catalyst activity at low temperature first increased and then decreased with the increase of space velocity. Catalyst for a short time put little effect on the catalytic and thermal stability.3. In the reverse flow catalytic combustion system, the optimum operational parameters were 800～3920mg/m3 of toluene concentration,2000 h-1～12000h-1 of space velocity and 2～10 min of periodic duration. The space velocity and toluene concentration had a significant effect on heat wave velocity. The peak temperature of heat waves and the average temperature of the reactor were increased with the increase of toluene concentration , increased with the decrease of periodic duration,and first increased and then decreased with the increase of space velocity. Compared with a fixed bed reactor, toluene conversion in a reverse flow reactor was higher, above 96.5%.